Currently, various methods are being used to combat the concern regarding concealed explosive substances. Some of these methods include: metal detectors, vapor detectors, X-ray machines, and dogs. Many countries are putting forth great efforts in developing new methods for inspection of the human body based on new physical principles including: Raman backscattering, dielectric portals, passive and active terahertz range devices, passive millimeter range radars, and active microwave portals.
The aforementioned methods do not guarantee the required effectiveness of remote and covert inspection; thus, these devices are not capable of detecting a “suicide bomber” in adequate time so that the necessary precautions can be taken before detonation of the explosive device occurs. Another notable disadvantage of the current methods is the lack of automatic determination of the threat level of a detected object as well as a high false alarm rate. These obstacles make it nearly impossible to use such devices, e.g., for inspection of a large number of people moving in transit.
One current method of detection used for metallic and non-metallic explosive devices concealed on a person is as follows: The receiving antenna focuses on a small area of the human body using electromagnetic waves coming from that region. A radiometer data is then processed in a processing module, and the intensity and position of the beam is recorded. The measured intensity of the received signal is then displayed as luminous intensity. By analyzing the distribution of the luminous intensity, the presence or absence of metallic or non-metallic objects can be determined. The main disadvantage of this method is the low contrast of the received image. This method cannot clearly distinguish non-metallic objects from the human body while the dielectric for the used wave range is transparent.
There is a need for covert automatic (without operator) inspection of a crowd of moving people to unveil suicide bombers and separate them from the crowd.